Salman Abedi, a 22-year-old Briton of Libyan descent, blew himself up as fans were leaving Grande's concert in the northwest England city on May 22, 2017. Twenty-two concertgoers were killed, and police say more than 800 people were left "with physical and deep psychological injuries."

On the anniversary, Manchester residents laid bouquets of flowers in the city's St. Ann's Square, or left hand-written notes on Japanese maples that have been planted to form a "Trees of Hope" trail through the city. One note cited U.S. Episcopal bishop Michael Curry's sermon at Saturday's royal wedding: "As a clever bishop said 'there is power in love.'"

Greater Manchester Mayor Andy Burnham said it was a day to "come together."

Thousands of people paused outside Manchester Cathedral at 2:30 p.m. for a minute of silence that was observed across the country — including in Parliament, where lawmakers paused their debates and fell still.

Prince William and Prime Minister Theresa May joined survivors and emergency workers who responded to the attack for a remembrance service at the cathedral.

A choir sang "Amazing Grace" and "Somewhere Over the Rainbow," and Christian, Jewish, Hindu, Sikh, Muslim and humanist leaders all addressed the congregation.

William read a passage from the Bible's book of Corinthians, ending: "Faith, hope and love abide, these three; but the greatest of these is love."

Later, thousands of people — including a choir of survivors — are due to gather for a sing-song in the city's St. Ann's Square. The event will include renditions of Grande's "One Last Time" and "Look Back In Anger" by Oasis, which became an unofficial anthem of Manchester after the attack.

Bells on the city hall and churches will ring out at 10:31 p.m., a year since the bomb exploded.

Police say 100 investigators are still working on the case. The U.K. has issued an arrest warrant for Abedi's younger brother, Hashem Abedi, and is seeking his extradition from Libya — a far-from-straightforward process given that country's political chaos.